Reverse transcription (RT) of the tyrosinase mRNA and specific cDNA amplification by nested polymerase chain reactin (PCR) have been reported to facilitate the early detection of circulating tumor cells in melanoma patients. The significance and practical value of this procedure for the diagnosis of tumor dissemination in melanoma patients are unclear. In the current study we analyzed peripheral blood samples of 65 melanoma patients of different clinical stages for the presence of tyrosinase mRNA by RT-PCR using nested oligonucleotide primers specific for tyrosinase cDNA. Furthermore, blood samples were evaluated for tumor cell growth by cell culture assays in vitro. No tyrosinase mRNA was detectable in blood samples of 26 patients with primary melanoma and 16 patients with regional lymph node metastases. In five of 13 patients with visceral metastases we found at least one blood sample positive for tyrosinase mRNA during a 2-to 4-mo interval. Analyses of different blood samples of patients with visceral metastases taken in a 2-h interval, furthermore, indicate that tumor cells only transiently persist in the peripheral blood. We obtained in vitro proliferating melanoma cells from two blood samples derived from different patients with visceral melanoma metastases. This demonstrates that viable melanoma cells indeed circulate in the peripheral blood with retained proliferative capacity in vitro. The analysis of blood samples by RT-PCR for tyrosinase mRNA, however, is not suitable for the early detection of tumor progression in melanoma patients.